User interfaces on digital information processing devices often have more information and options than can be easily handled with buttons or other physical controls. In particular, scrolling of documents and data, selection of menu items, and continuous value controls, such as volume controls, can be difficult to control with buttons and general purpose pointing devices. These buttons and pointing devices are inherently limited in how far they can move or how many options can be selected. For example, a computer mouse, though it can move a pointer or cursor indefinitely, has limits to how far it can move without being picked up and repositioned, which limits its usability in these situations.
Solutions to this problem have included:                a. Keys, such as “page up” and “page down” and arrow keys, that are specifically designated to maneuver through or control data;        b. Provisions for scrollbars in a user interface which can be used to scroll data long distances by using a standard computer pointing device controlling a cursor;        c. Similarly controlled (as in b.) hierarchical menus or choices;        d. Graphical user interface elements such as “slider bars” and “spin controls” to vary a parameter over an arbitrary range;        e. Scrolling “wheels” on standard pointing devices;        f. Physical knob controls, which, when used to control a user interface are often referred to in the art as “jog dials”. Some knobs and dials output quadrature signals to indicate direction of motion;        g. Trackballs that rely on optically or mechanically sensed spherical controls to provide two-dimensional sensing; and        h. A capacitive two-dimensional object position sensor that can be used for scrolling by providing a “scrolling region”, where users can slide their fingers to generating scrolling actions.        
The disadvantages of these prior solutions are as follows:                a. Designated Keys: These typically require designated space on the keyboard as well as supporting electronics and physical structures. Keys usually limit the control they offer to the user over the information being scrolled or the function being performed to distinct values. For example, page up and page down keys enable the user to increment through a document at a constant rate of page by page only.        b. Scroll bars controlled by a pointing device and a cursor: These elements require the user to move long distances across a display and/or select relatively small controls in order to scroll the data. Additionally, these scroll bars take up room on the display that can be used for other purposes.        c. Hierarchical menus controlled by a pointing device or by key combinations: These have a similar problem to scroll bars, in terms of the complexity of the targeting task that faces the user. First, the user must hit a small target near the edge of a screen, and then the user must navigate along narrow paths to open up additional layers of menu hierarchy. Shortcut keys, which usually consist of key combinations, are typically non-intuitive and hard to remember.        d. “Sliders” and “spin controls” controlled by a pointing device or by key combinations: These have targeting problems similar to scroll bars and hierarchical menus (sometimes exacerbated by the targets usually being even smaller than in the cases of scrollbars and menus).        e. Physical Scroll Wheels on mice: The user is unable to scroll very far with these wheels due to mechanical limitations in how far the user can move the wheel in a single stroke. These mechanical limitations are because of the construction of the wheel itself or because of interactions between the wheel and nearby physical features (such as the wheel mounting or the device housing). The limits on the practical/comfortable length of the basic finger motion also severely restrict the ability of the user to scroll significant distances in one stroke. Additionally, these wheels are mechanically complex and take up a lot of space.        f. Physical knobs or “Jog Dial” controls: These have the disadvantages of being relatively large and mechanically complex. Similar to the scroll wheel, the knob or dial requires some amount of friction to limit accidental activation, which increases the difficulty of fine adjustments. Additionally, it is difficult to use a physical knob or dial with a great degree of accuracy, and the knob or dial inherently has inertia that may cause overshoot in large motions. The physical knobs or dials are often mechanically limited in range of rotation imposed by the construction or by the interactions of the knob or dial with nearby physical features.        g. Trackballs: These are similar to the physical knobs in that they have the disadvantages of being bulky and mechanically complex. The trackball is difficult to use with a great degree of accuracy, and the trackball inherently has inertia that may cause overshoot in large motions. Additionally, the trackball presents additional complexity in that it presents control of two dimensions of motion in a way that makes it difficult for users to limit their inputs to a single dimension. Finally, the input is limited either by the construction of the trackball and its housing, or by natural limits on comfortable/practical finger motion, or both.        h. Scroll Regions: These are limited by the physical limitation that a user's finger will eventually reach the end of the scrolling region and the user will have to lift their finger, replace it on the sensor inside the region, and continue the motion. The user must perform many repetitive motions of the same finger to scroll long distances with a scroll region.        
The disadvantages of the prior art can be remedied by devising a user interface that enables scrolling, selecting, and varying controls over a long range of possible positions and values.